This invention claims priority of the German patent application 100 61 627.542 filed Dec. 11, 2000 and of the German patent application DE 101 54 240.2 filed Nov. 7, 2001 which are incorporated by reference herein.
The invention concerns a microscope with a capability for switching between the deep ultra-violet and the visible spectral region, having a displaceable tube lens changer with at least one tube lens for the deep ultra-violet spectral region and at least one tube lens for the visible spectral region.
The resolution of a microscope depends substantially on the wavelength of the illumination light used. Conventional microscopes are operated with light in the visible wavelength region (abbreviated xe2x80x9cVISxe2x80x9d). In order to resolve extremely small structures, for example on wafers or circuits in the semiconductor industry, imaging at shorter wavelengths in the deep ultra-violet of the light spectrum (abbreviated xe2x80x9cDUVxe2x80x9d) is required. The microscope image is made visible using a TV camera that is sensitive to the DUV light.
The materials in conventional VIS optics which are suitable for the VIS spectral region are not transparent to DUV. DUV operation of the microscope therefore requires optics constructed from special materials, for example prisms, beam splitters, and tube lenses, as well as objectives that are corrected for DUV wavelengths. In order to meet future requirements of the semiconductor industry, a DUV microscope preferably has capabilities for switching between VIS and DUV optics and the respective associated illumination systems, in which a switchover between VIS and DUV objectives is also made.
Nowadays, the objectives of most manufacturers, which have a high correction rate of all image errors, are calculated for an infinity beam, and together with a tube lens constitute a compensation system. This means, by correction of the image errors a first portion of the image errors is corrected in the objective and the remaining portion of the image errors is corrected in the tube lens. Accordingly, it is not essential that a tube lens consists of a single lens, as the term lets presume, but can consist of lens groups or a tube lens system. Therefore, for different objectives which are calculated for different spectral regions, the relevant compensating tube lens has to be inserted into the beam path for the related objective and the related spectral region. Such a compensating system consisting of an objective and a tube lens is, for example, described in German patent application DE 199 31 949 A1.
In a microscope with a capability for switching between the deep ultra-violet and the visible spectral region, the compensation must be made for the chosen spectral region. Therefore, a switch-over to the chosen spectral region requires that the tube lens changer is also changed to the corresponding tube lens.
In known microscopes that are designed for working in both the UV and the visible light region, different reflectors and filters which are assigned for different microscopy and contrast methodsxe2x80x94for example bright-field, dark-field, interference contrast, and DUV methodsxe2x80x94are arranged shiftably in the illuminating beam path and mounted on a reflector carrier. Displacement can be accomplished by hand or preferably by a motorized drive system.
Depending on the adjustment of the microscope, a tube lens has not only to be attached to a certain objective, but additionally to a certain reflector or filter. In the known microscopes, the displacement of the tube lens changer is accomplished by way of a separate motorized drive system for the tube lens changer. The association between the motorized shiftable reflectors on the one hand and a corresponding tube lens on the other hand is accomplished by software.
Disadvantages of this known displacement and association of the tube lens changer and tube lens are on the one hand the complex and space-intensive use of a motorized drive system for the tube lens changer, and on the other hand the circumstance that a program fault or program failure can result in an incorrect association between reflector and tube lens when working in the UV light region.
It is therefore an object of the invention to create a microscope with a simple and safe capability for switching between the deep ultra-violet and the visible spectral region.
This object is achieved, according to the present invention, in that the reflector carrier on the one hand and the tube lens changer on the other hand are mechanically coupled to one another in such a way that shifting the reflector carrier in the illuminating beam path to a specific reflector automatically displaces the tube lens changer in such a way that the latter arranges in the optical axis a tube lens corresponding to the reflector.
As a result of the mechanical positive coupling according to the present invention between the motion of the reflector carrier and that of the tube lens changer, a separate drive system for the tube lens changer can be dispensed with. The mechanical coupling of the two assemblies is moreover designed in such a way that, for example, a UV tube lens is automatically associated with the DUV reflector with no need for a separate and thus also fault-susceptible software-based or similar association of the assemblies with one another.
According to a practical embodiment of the invention, it is proposed that the positive coupling between reflector carrier and tube lens changer be accomplished via at least one driver pin which is configured as a pin, retained on the reflector carrier, that engages into a corresponding receptacle of the tube lens changer and positively drives the latter upon displacement of the reflector carrier.
The tube lens changer is advantageously configured in space-saving fashion as a rotatably mounted disk whose rotation angle for shifting the tube lens into the optical axis can be limited by way of adjustable stops.
In order to hold the tube lens changer and thus the tube lenses in accurately positioned fashion in the end positions of the rotation angle, it is further proposed that in the end positions, the tube lens changer be spring-loaded in the direction of the stops.
For configuration of the reflector carrier, the invention proposes that the latter be configured as a linear slider, since such a slider can be moved in reliable and accurately positioned fashion along a linear guide. This is of even greater importance in the present case because, as a result of the positive coupling, the motion of the reflector carrier directly brings about the displacement of the tube lens changer.
Lastly, the invention proposes that the linear slider be drivable in motorized fashion.